I believe it was mentioned in the past that in order to keep the frame rate and graphics up to Project CARS standards, they avoided split screen as that would have reduced performance. So no, split screen is not available.

EDIT: Here is an excerpt from the FAQ: http://www.projectcarsgame.com/faq.html

Is there a split screen mode?
In order to achieve the target of 60 frames per second, there is no split screen mode in Project CARS